1. Field of the Invention
The present invention belongs to a technical field of a printer, a copy machine, a multi-function machine or other image forming apparatuses, and particularly relates to a cleaning technology for removing toner or other deposits remaining on an image carrier.
2. Description of the Related Art
As an image carrier, a photosensitive drum has been widely used in an electrophotographic image forming apparatus such as a copy machine and a printer. In the image forming apparatus that uses the photosensitive drum, a charging device uniformly charges the circumferential surface of the photosensitive drum to a predetermined potential, and then, based on image data, part of the potential is optically attenuated by irradiating the circumferential surface of the photosensitive drum with an LED of an exposure device to form an electrostatic latent image corresponding to an image on an original document. Then, a toner image is formed on the circumferential surface of the photosensitive drum by developing this electrostatic latent image using a developing device. The toner image is transferred to a paper sheet when the paper sheet passes through a transfer region that is configured by bringing the photosensitive drum into contact with, or close to, a transfer member.
In this type of image forming apparatus, after transferring the toner image to the paper sheet some toner often remains deposited on the circumferential surface of the photosensitive drum without being transferred to the paper sheet. The photosensitive drum needs to be cleaned because the residual toner on the circumferential surface of the photosensitive drum stands in the way of subsequent new image formation. A variety of cleaning methods are widely known. Examples of the cleaning methods used here include a method of pressing a cleaning roller, rotating brush, or other rotary member to the circumferential surface of the photosensitive drum to move and collect the residual toner to the rotary member, a method of bringing a cleaning blade into contact with the circumferential surface of the photosensitive drum to scrape the residual toner off the circumferential surface of the photosensitive drum, and a method that combines these cleaning methods.
On the other hand, when an amorphous silicon photoreceptor is used as a photoreceptor, discharge products produced by the discharge of the charging device are easily deposited onto the circumferential surface of the amorphous silicon photoreceptor. The electric resistance of the circumferential surface of the photoreceptor decreases as the discharge products absorb the moisture, causing image deletion that disturbs the electrostatic latent image. There is thus known a method of adding a small amount of abrasive to a toner, carrying the toner on the circumferential surface of a cleaning roller, and causing this toner to grind the discharge products deposited on the circumferential surface of the photoreceptor.
A first known technology has a magnetic brush for grinding the surface of a photosensitive drum and a light quantity sensor for detecting the quantity of surface-reflected light of the photosensitive drum, wherein the magnetic brush is operated according to the value of the quantity of surface-reflected light of the photosensitive drum other than when forming an image.
A second known technology aims to effectively remove foreign matters deposited on the circumferential surface of a photosensitive drum, even when the image area ratio varies with each part of the circumferential surface of the photosensitive drum. In this technology the photosensitive drum is divided into six blocks in a main scanning direction, and the number of dots being written is counted for each of the six blocks until the rotating time of the photosensitive drum reaches a predetermined time. Then, the image area ratio of each block is obtained. Regarding the blocks with the image area ratios that are equal to or lower than a reference value, an electrostatic latent image with a predetermined toner consumption pattern is formed on the photoreceptor, toner is then deposited by developing means, and the toner is forcibly cleaned using cleaning means.
In the image forming apparatus using the first technology, the quantity of surface-reflected light of the photosensitive drum is measured, and then the magnetic brush is operated based on the measured value. Consequently, scraping the film of the photosensitive drum causes fluctuations in the quantity of surface-reflected light, and the light quantity sensor becomes dirty as the toner scatters, reducing the detection accuracy of the light quantity sensor. Furthermore, when the quantity of surface-reflected light cannot be detected in the entire axial direction of the photosensitive drum, the operation for grinding the surface of the photosensitive drum by using the magnetic brush might not be able to be carried out when necessary, or the operation for grinding the surface of the photosensitive drum by using the magnetic brush might be performed even when unnecessary.
In the image forming apparatus using the second technology, the toner is supplied to a section that is not printed, as a countermeasure to poor grinding, as well as for the purpose of preventing bending of the cleaning brush due to the reverse rotation thereof or preventing clogging. The problem, therefore, is the increase in toner consumption. There is also known a technology for reversely rotating the cleaning roller to increase its grinding force, wherein when the cleaning roller is reversely rotated without supplying the toner in order to suppress toner consumption, polishing is not performed sufficiently, causing an image defect.